1. Field of the Invention
A certain aspect of this disclosure relates to a cooling device and an image forming apparatus including the cooling device.
2. Description of the Related Art
An image forming apparatus such as a printer, a facsimile machine, or a copier normally includes an optical unit, a scanning unit, a fusing unit, and a developing unit that generate heat, and the generated heat increases the temperature in the image forming apparatus.
For example, when a developer agitating/conveying part of the developing unit is driven to agitate and convey a developer in the developing unit, the temperature in the developing unit is increased due to frictional heat generated by friction between the developer and the developer agitating/conveying part and friction among developer particles. Frictional heat is also generated by friction between a developer and a developer-thickness limiting part that limits the thickness of a layer of the developer on a developer carrier before the developer is conveyed to a developing area. Further, when the layer of the developer is scraped by the developer-thickness limiting part, frictional heat is generated by friction among developer particles. Accordingly, such frictional heat also increases the temperature in the developing unit.
The increased temperature may cause toner in the developer to melt and stick to the developer-thickness limiting part, the developer carrier, and an image carrier; and the sticking toner may cause an image error such as an undesired white line in an image. Also, when stress such as pressure or frictional force is applied to heated toner, an external additive on the toner surface may be buried in the toner or removed from the toner surface and as a result, the toner may harden on the carrier. Over time, the above problems may degrade the performance of the developing unit. Particularly, when toner with a low melting temperature is used to reduce the energy necessary for fusing, image errors may easily occur due to sticking and hardening of toner.
In a known image forming apparatus, external air is drawn into the image forming apparatus with an air-cooling fan and conveyed via a duct to an area near the developing unit to generate an air current and thereby to cool the developing unit. This configuration makes it possible to prevent the temperature of the developing unit from increasing excessively. However, with a recent downsized, densely-packed image forming apparatus, it is difficult to secure a space around a developing unit to install a duct for circulating air from a cooling fan to cool the developing unit.
Meanwhile, Japanese Patent Application Publication No. 2005-164927 discloses an image forming apparatus including a liquid-cooling device that circulates a liquid to cool a developing unit. The disclosed liquid-cooling device includes a heat-receiving part that is in contact with a surface of the developing unit so that a cooling liquid can receive heat from the developing unit; a radiation unit for transferring heat from the cooling liquid; a tube laid out such that the cooling liquid circulates between the heat-receiving part and the radiation unit, and a conveying unit for conveying the cooling liquid through the tube. Generally, a liquid-cooling device can cool a developing unit more efficiently than an air-cooling device. Also, since the cross section of a tube for circulating a cooling liquid is generally smaller than the cross section of a duct for circulating cooling air, the tube for circulating a cooling liquid can be laid out around a developing unit even when only a small space is available around the developing unit. Thus, a liquid-cooling device can be used to cool a developing unit even in a densely-packed image forming apparatus.
As described above, an image forming apparatus includes components (hereafter called temperature-increasing parts), such as an optical unit, a scanning unit, a fusing unit, and a developing unit, the temperatures of which increase during an image forming process. Such temperature-increasing parts are present in various parts of an image forming apparatus, and a liquid-cooling device is preferably used to cool the temperature-increasing parts. When using a liquid-cooling device for a densely-packed image forming apparatus where only small space is available, it is necessary to lay out a tube in a complex pattern through the small space and provide heat-receiving parts for respective temperature-increasing parts. Therefore, when installing or removing a liquid-cooling device in or from an image forming apparatus, it is necessary to separate the tube of the liquid-cooling device into parts. When separating a tube containing a cooling liquid into parts, it is preferable to completely drain the cooling liquid from the tube to prevent the cooling liquid from spilling out of the tube. However, a tube laid out in a complex pattern in an image forming apparatus includes parts, such as U-shaped parts, where the cooling liquid tends to remain, and therefore it is difficult to completely drain the cooling liquid from the tube. Accordingly, if the tube is separated at positions where the cooling liquid tends to remain, a large amount of the cooling liquid spills out of the tube and wets the interior of the image forming apparatus and the floor.